1. Field of the Invention
The present invention relates generally to corrective control system and method for a liquid pressure control apparatus in, for example, a vehicular automatic transmission which accurately control an output liquid pressure in accordance with a value of an electrical signal and, more particularly, relates to the corrective control system and method which control correctively the output liquid pressure of a control valve unit equipped within the vehicular automatic transmission.
2. Description of the Related Art
In the control valve unit of the vehicular automatic transmission, the electrical signal is used to drive a solenoid so as to produce a signal pressure in accordance with the electrical signal. This signal pressure is used to make a gear shift by controlling a clutch pressure of a frictional element which is the output liquid pressure and a line pressure which is an original pressure of the clutch pressure of the frictional element. At this time, due to a variation in a circuit resistance and a difference in performance between the individual products of frictional elements and solenoids, a relationship between the electrical signal for driving the solenoid and the output liquid pressure cannot accurately be obtained. Both of a shift shock and a response delay in the gear shift easily occur. Thus, desired action and advantages cannot accurately be obtained.
A Japanese Patent Application First Publication No. 2001-116130 published on Apr. 27, 2001 exemplifies a previously proposed corrective control system for a liquid pressure control apparatus in which an actual relationship between the electrical signal for the drive of the solenoid and the output liquid pressure due to the variation in the circuit resistance and difference in performance between individual products of frictional elements and solenoids is compared with each of a plurality of prepared maps having various characteristics. By selecting one of the maps which is least deviation from the actual relationship, an accuracy in the relationship between the solenoid drive electrical signal and the output liquid pressure is improved and an improvement in a controllability can be achieved. Specifically, the actual output pressures with respect to the electrical signals at a plurality of points preset are measured. Thereafter, with a lateral axis as output values on the map and with a longitudinal axis as an actual output liquid pressure, the actual output liquid pressures are plotted. The plotted values are approximated to a first-order function through a least square method. This approximated first-order function has a gradient (gain) and a constant term (offset). These gradient value and constant term are stored. Then, during an actual control procedure, a target output liquid pressure is substituted into the longitudinal axis to calculate an instantaneous map output (liquid) pressure from the stored gain and offset values.
FIG. 7 shows a structure for creating the output liquid pressure which is the clutching pressure of a certain frictional element (or brake) of the automatic transmission from the signal pressure that a solenoid outputs. The previously proposed liquid pressure control apparatus includes: a solenoid valve 40 which creates a spool pilot pressure PS-PLT from a pilot pressure PPLT and a spool valve 50 outputting a liquid supply pressure P for the frictional element or the brake from line pressure PL which is the spool supply pressure according to the spool pilot pressure PS-PLT. In solenoid valve 40, a movement quantity of a plunger 42 is increased in accordance with a supply current value. A spherical ball 43 is moved which, for example, interrupts pilot pressure PPLT and spool pilot pressure PS-PLT so that a flow passage 44 is opened. Then, pilot pressure PPLT is communicated with spool pilot pressure PS-PLT so that a spool pilot pressure PS-PLT is increased. On the other hand, in spool valve 50, a spool supply pressure (line pressure valve) is communicated with a frictional element. This spool 51 is moved together with a pressure increase in spool pilot pressure PS-PLT opposed against spool spring 52 and the flow passage is closed so that line pressure PL which is the spool supply pressure reduces the frictional element supplying pressure. Hence, when a current value caused to flow through solenoid valve 40 is large, spool pilot pressure PS-PLT and frictional element supplying pressure P is decreased linearly.
In the case of the solenoid valve described above, an output (liquid) pressure characteristic is exhibited which is different from spool pilot pressure PS-PLT which is an output (liquid) pressure of the solenoid due to the characteristic of a spool spring 52. FIG. 6 shows characteristic graphs representing a static characteristic of the relationship between the drive current to the solenoid and output liquid pressure. As shown in FIG. 6, a, so-called, hysterisis characteristic is exhibited between the drive current and the output liquid pressure. Hence, the prepared map is used which is an average output liquid pressure value at each current value from a static characteristic as denoted by a dot line shown in FIG. 6.
However, a deviation of the average output liquid pressure prepared map for each spaced apart current value described above from the actual output (liquid) pressure characteristic occurs and a worsening of the controllability will be introduced. Especially, in a region of the hysterisis characteristic (a nonlinear characteristic region) in which the current value is large but the output liquid pressure is small, a point of inflection is shifted toward a higher output (liquid) pressure side than an actual characteristic thereof. For example, in a case where the current value is raised and, in a midway through a remarkable rise of the current value, the current value is once reduced, the output (liquid) pressure is lowered and follows along a loop of a current rise side (refer to FIG. 6) (hereinafter, referred to a first hysterisis loop) of a hysterisis curve is the static characteristic of the actual output (liquid) pressure and, thereafter, when the current value is lowered, the output (liquid) pressure does not follow along a second hysterisis loop of a current value reduction side (output (liquid) pressure rise side) but traces a value of the output line pressure shifted toward a lower output (liquid) pressure side. Especially, such a phenomenon as described above becomes remarkable in such a hysterisis characteristic that when the output pressure is, at a stroke, reduced in accordance with the increase in the current value and when the output pressure is, at the stroke, increased in accordance with the decrease in the current value.
In addition, in the above-described Japanese Patent Application First Publication, it is possible to accurately correct the current value of the electrical signal to drive the solenoid in a case where the electrical signal is supplied to such a control valve unit as to have a similarity characteristic as any one of the plurality of prepared (preset) maps having the various characteristics and have a characteristic of the current value shifted toward an output pressure increase direction. However, the correction of the current value is not carried out in a case where the electrical signal is supplied to such a control valve unit as to have the similarity characteristic as any one of the maps and have a characteristic of the current value shifted toward a current value increase direction. However, a sufficient correction value cannot be obtained. Hence, it may be considered that a high-order function can be used to approximate the relationship between the output (liquid) pressure actually measured value and the output pressure actually measured value and the output pressure threshold value in place of, for example, a least square method. However, a calculation burden is large and is not practical. In addition, it may be considered that maps are newly added. However, a memory capacity by the number of maps added is needed to be increased and the manufacturing cost is accordingly increased.
It is, hence, an object of the present invention to provide corrective control system and method for a liquid pressure control apparatus which are capable of improving the controllability even if a large hysterisis occurs between the electrical signal and output pressure caused by performance deviations in a liquid pressure circuit and solenoid of the control valve unit and are capable of compensating the deviation with a small memory capacity even if the deviation caused by the above-described deviation of characteristic in liquid pressure circuit resistance and the individual performance difference of the products described above.
The above-described object can be achieved by providing a corrective control system for a liquid pressure control apparatus of a control valve unit, comprising: a liquid pressure controlling section that controls an output liquid pressure of the control valve unit on the basis of a current value which is an electrical signal generated in accordance with an output pressure demand value P* determined according to a calculation process executed within a control unit; an output liquid pressure actually measuring section that outputs respectively separated current values to a solenoid drive circuit of the control valve unit and actually measures the output liquid pressure values for the outputted respective current values; an output pressure theoretical value calculating section that calculates an output liquid pressure theoretical value for each of the current values outputted by the actually measuring section by referring to preset fundamental maps, each fundamental map representing a relationship between the current value and the output liquid pressure theoretical value; fundamental map presetting section that presets the fundamental maps on the basis of a hysterisis characteristic that each individual control valve unit has, the hysterisis characteristic being exhibited in such a manner that the output liquid pressure actually measured value which takes along a first hysterisis loop when the current value is increased toward a larger value is different from that which takes along a second hysterisis loop when the current value is, in turn, decreased toward a smaller value from the larger value; a corrective term calculating section that approximates a relationship between the output liquid pressure actually measured value and the output liquid pressure theoretical value for each of the same current values to a first-order function and calculates a coefficient of the approximated first-order function and a constant thereof; a storing section that stores the calculated coefficient and constant therein; and a correcting section that corrects the electrical signal which accords with the output liquid pressure demand value on the basis of the coefficient and constant stored in the storing section, wherein each of the fundamental maps referred to by the output liquid pressure theoretical value calculating section is a map representing a relationship between the output liquid pressure actually measured value and a current average value, the current average value being calculated to be an average of the current between the current value in the first hysterisis loop of the hysterisis characteristic and that in the second hysterisis loop thereof with respect to each of the same output pressure actually measured values.
The above-described object can also be achieved by providing corrective control method for a liquid pressure control apparatus for a control valve unit, comprising: controlling an output liquid pressure of the control valve unit on the basis of a current value which is an electrical signal generated in accordance with an output pressure demand value P* determined according to a calculation process executed within a control unit; outputting respectively separated current values to a solenoid drive circuit of the control valve unit; actually measuring the output liquid pressure values for the outputted respective current values; calculating an output liquid pressure theoretical value for each of the outputted current values by referring to preset fundamental maps, each fundamental map representing a relationship between the current value and the output liquid pressure theoretical value; presetting the fundamental maps on the basis of a hysterisis characteristic that each individual control valve unit has, the hysterisis characteristic being exhibited in such a manner that the output liquid pressure actually measured value which follows along a first hysterisis loop when the current value is increased toward a larger value is different from that which follows along a second hysterisis loop when the current value is, in turn, decreased toward a smaller value from the larger value; approximating a relationship between the output liquid pressure actually measured value and the output liquid pressure theoretical value for each of the same current values to a first-order function; calculating a coefficient of the approximated first-order function and a constant thereof; storing the calculated coefficient and constant therein; and correcting the electrical signal which accords with the output liquid pressure demand value on the basis of the stored coefficient and constant, wherein each of the fundamental maps to be referred to when calculating the output liquid pressure theoretical value is a map representing a relationship between the output liquid pressure actually measured value and a current average value, the current average value being calculated to be an average of the current between the current value in the first hysterisis loop of the hysterisis characteristic and that in the second hysterisis loop thereof with respect to each of the same output pressure actually measured values.
This summary of the invention does not necessarily describe all necessary features so that the invention may also be a sub-combination of these described features.